I know that when I permanently delete something from Outlook (so also from the Deleted Items folder), it will still not be deleted directly and my pst-file won’t become smaller unless I run Compact Now. Until then or until it gets overwritten, the data is still stored within the pst-file and thus recoverable as you described here.

I’d prefer the deleted items to be really gone and free up space directly. For this I now manually run Compact Now a couple of times per week.

Can I configure Outlook that it will always automatically compact the pst-file whenever I delete something?